1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming method, and an intermediate transfer member using an electrophotographic process. In particular, the present invention relates to an image forming apparatus, an image forming method, and an intermediate transfer member, in which a toner image formed on a first image holding member is transferred onto an intermediate transfer member and then retransferred onto a second image holding member.
2. Description of the Related Art
Image forming apparatuses having intermediate transfer members have the following advantages compared with image forming apparatuses that perform a direct transfer of an image from a first image holding member onto a second image holding member which is gripped or adsorbed onto a transfer drum (as described in, for example, Japanese Patent Laid-Open No. 63-301960). There will not be any significant registration occur when different color images are overlapped; and the selection of possible materials and the shapes of the second image holding member have high versatility since it can be used without additional treatment and control, for example, being fixed with a gripper, by adsorption, or by curling itself. For example, a usable second image holding member ranges from a thin paper sheet of 40 g/m.sup.2 to a thick paper sheet of 200 g/m.sup.2. Further, its length and width are not limited. Envelopes, postcards and labels can therefore be used as a second image holding member. Full-color copying machines and printers provided with intermediate transfer systems having such advantages are spreading.
The recent rapid spread of image readers for personal computers, digital cameras and image scanners has led to a great demand for full-color printers and copying machines. These printers and copying machines must be applicable to a variety of users and environments. Other requirements are that the costs of producing, operating and maintaining are low, that maintenance is easy, that the apparatus itself is miniaturized, and that stability of the image quality is not affected by environmental factors, such as temperature and humidity.
Key factors for satisfying such requirements are the characteristics involved in transferring images from an intermediate transfer member to a second image holding member such as a paper sheet (hereinafter the transfer is referred to as secondary transfer), and cleaning characteristics of a developer remaining on the intermediate transfer member after the secondary transfer. The cleaning characteristics greatly affect the life of the intermediate transfer member, the configuration of the apparatus body, and the maintenance operation. Further, the transfer characteristics greatly affect the quality of the image and la the cleaning operation. The transfer characteristics will deteriorate significantly under a high-temperature, high-humidity environment.
A means for improving the transfer characteristics is disclosed in Japanese Patent Laid-Open No. 7-234592, in which fine particles being less than half the size of toner particles, are fixed onto the elastic surface of the intermediate transfer member in order to improve releasability. In Japanese Patent Laid-Open No. 9-230717, an intermediate transfer member which is coated with beads having a certain diameter is disclosed. Other means include the formation of a coating layer composed of water-repellent resin and the use of a water-repellent resin belt. Another means for improving the transfer characteristics is to use a copying machine provided with a coating unit which applies a lubricant onto the intermediate transfer member as disclosed in Japanese Patent Laid-Open No. 8-248776.
None of these means, however, have a countermeasure to the deterioration of transfer characteristics under high-temperature, high-humidity environments.